A study of the rapid rotator $\zeta$ Aql: differential surface rotation?

Abstract

We report new, extremely precise, photopolarimetry of the rapidly-rotating A0 main-sequence star $\zeta$ Aql, covering the wavelength range $\sim$400--900nm, which reveals a rotationally-induced signal. We model the polarimetry, together with the flux distribution and line profiles, in the framework of Roche geometry with $\omega$-model gravity darkening, to establish the stellar parameters. An additional constraint is provided by TESS photometry, which shows variability with a period, $P_{\mathrm{phot}}$, of 11.1 hr. Modelling based on solid-body surface rotation gives rotation periods, $P_{\mathrm{rot}}$, that are in only marginal agreement with this value. We compute new ESTER stellar-structure models to predict horizontal surface velocity fields, which depart from solid-body rotation at only the $\sim$2% level (consistent with a reasonably strong empirical upper limit on differential rotation derived from the line-profile analysis). These models bring the equatorial rotation period, $P_{\mathrm{rot},\mathrm{e}}$, into agreement with $P_{\mathrm{phot}}$, without requiring any 'fine tuning' (for the Gaia parallax). We confirm that surface abundances are significantly subsolar ($\mbox{[M/H]} \simeq -0.5$). The star's basic parameters are established with reasonably good precision: ${M = 2.53\pm0.16\,\mbox{M}_\odot}$, $\log{L/\mbox{L}_\odot} = 1.72\pm0.02$, $R_{\rm p} = 2.21\pm 0.02\,\mbox{R}_\odot$, $T_{\rm eff} = 9693 \pm 50~\mbox{K}$, $i=85{{}_{-7}^{+5}}^{\circ }$, and $\omega /{\omega }_{\mathrm{c}}=0.95\pm 0.02$. Comparison with single-star, solar-abundance stellar-evolution models incorporating rotational effects shows excellent agreement (but somewhat poorer agreement for models at $\mbox{[M/H]} \simeq -0.4$).

arXiv commentMNRAS, accepted Minor typographical edits in v3

References in corpus (41)

• The Transiting Exoplanet Survey Satellite
• Validation of the new Hipparcos reduction
• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms
• Gaia Early Data Release 3: Parallax bias versus magnitude, colour, and position
• Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 parsecs: The Northern Sample I
• Gaia Early Data Release 3 -- Catalogue validation
• The VAST Survey - III. The multiplicity of A-type stars within 75 pc
• Be-star rotation: how close to critical?
• Gravity darkening in rotating stars
• Rotational velocities of A-type stars II. Measurement of vsini in the northern hemisphere
• Gaia Early Data Release 3: Summary of the contents and survey properties
• Coude-feed stellar spectral library - atmospheric parameters
• Stellar Diameters and Temperatures I. Main Sequence A, F, & G Stars
• Theory and evidence of global Rossby waves in upper main-sequence stars: r-mode oscillations in many Kepler stars
• Self-consistent 2D models of fast rotating early-type star
• New measurements of rotation and differential rotation in A-F stars: Are there two populations of differentially rotating stars?
• Differential rotation in K, G, F and A stars
• New limb-darkening coefficients and synthetic photometry for model-atmosphere grids at Galactic, LMC, and SMC abundances
• An algorithm for computing the 2D structure of fast rotating stars
• Resolving the Effects of Rotation in Altair with Long-Baseline Interferometry
• A high-sensitivity polarimeter using a ferro-electric liquid crystal modulator
• A near-infrared interferometric survey of debris disc stars. II. CHARA/FLUOR observations of six early-type dwarfs
• The linear polarization of nearby bright stars measured at the parts per million level
• Polarization measurements of hot dust stars and the local interstellar medium
• Polarization due to rotational distortion in the bright star Regulus
• The intrinsic and interstellar broadband linear polarization of nearby FGK dwarfs
• HIPPI-2: A Versatile High Precision Polarimeter
• The wavelength dependence of interstellar polarization in the Local Hot Bubble
• Stellar Photospheric Abundances as a Probe of Disks and Planets
• First signatures of strong differential rotation in A-type stars
• Rotating Convective Core Excites Non-Radial Pulsations to Cause Rotational Modulations in Early-Type Stars
• Overstable Convective Modes in Rotating Early Type Stars
• Be and Bn stars: Balmer discontinuity and stellar-class relationship
• Polarization of hot Jupiter systems: a likely detection of stellar activity and a possible detection of planetary polarization
• The rotation of alpha Oph investigated using polarimetry
• Detection of differential rotation in psi Cap with profile analysis
• Polarimetric and radiative transfer modelling of HD 172555
• A reappraisal of parameters for the putative planet PTFO 8-8695b and its potentially precessing parent star
• A study of the F-giant star $\theta$ Scorpii A: a post-merger rapid rotator?
• Non-linear excitation of low frequency modes by overstable convective modes in rotating stars

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